Recent reports describe avascular necrosis of the hip in patients with human immunodeficiency virus infection. This incidence, natural history, and cause are not understood. In this study, patients with no hip complaints will be offered magnetic resonance imaging of the hips. This will allow calculation of the prevalence of this abnormality. Predisposing causes will be sought. The natural history of radiologic lesions will be assessed. To date, 160 scans have been completed.